Title: Composition and automated crystal orientation mapping of rapid solidification products in hypoeutectic Al-4 at.%Cu alloys

Abstract

Rapid solidification can produce metastable phases and unusual microstructure modifications in multi-component alloys during additive manufacturing or laser beam welding. Composition and phase mapping by transmission electron microscopy have been used in this paper to characterize the morphologically distinct zones developing in hypoeutectic Al-4 at.% Cu alloy after pulsed laser melting for different crystal growth rate regimes. Deviations of the compositions of the alloy phases from equilibrium predictions and unique orientation relationships between the solidification transformation products have been determined. Specifically, for the columnar growth zone at solidification rates of 0.8 $\text{m}{\text{s}}^{-1}$ <$$ v $<{\text{v}}_{\text{a}}=1.8$ $\text{m}{\text{s}}^{-1}$, two distinct orientation relationships were established between the concomitantly forming non-equilibrium phases, supersaturated α-Al solid solution and the discontinuously distributed α-Al₂Cu-based θ'-phase, which can be described as {110}_θ $\parallel$ {001}_α, [001]_θ $\parallel$ [110]_α and {001}_θ $\parallel$ {001}_α, [100]_θ $\parallel$ [100]_α. These orientation relationships permit formation of coherent interphase interfaces with low interfacial free energy. Finally, this endows a kinetic advantage to the thermodynamically less stable θ'-Al₂Cu phase relative to the more stable equilibrium θ-Al₂Cu phase during formation of the morphologically modified eutectic of the columnar growth zone grains, since repeated nucleation is required to establish the discontinuous distribution of θ'-Al₂Cu phase.

Authors:

Zweiacker, K. W.  ^[1];

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Liu, Can ^[2]; Gordillo, M. A. ^[3]; McKeown, J. T. ^[4]; Campbell, G. H. ^[4]; Wiezorek, J. M. K. ^[2]

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1. Univ. of Pittsburgh, PA (United States). Dept. of Mechanical Engineering and Materials Science; Swiss Federal Laboratories for Materials Science and Technology (Empa), Dübendorf (Switzerland)
2. Univ. of Pittsburgh, PA (United States). Dept. of Mechanical Engineering and Materials Science
3. Univ. of Pittsburgh, PA (United States). Dept. of Mechanical Engineering and Materials Science; FEI Co., Hillsboro, OR (United States)
4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Materials Sciences Division

Publication Date:

Tue Dec 05 00:00:00 EST 2017

Research Org.:

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Univ. of Pittsburgh, PA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)

OSTI Identifier:

1438655

Alternate Identifier(s):

OSTI ID: 1496396

Report Number(s):

LLNL-JRNL-735845
Journal ID: ISSN 1359-6454

Grant/Contract Number:  

AC52-07NA27344; DMR 1105757; DMR 1607922; FWP SCW0974

Resource Type:

Accepted Manuscript

Journal Name:

Acta Materialia

Additional Journal Information:

Journal Volume: 145; Journal ID: ISSN 1359-6454

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; rapid solidification; TEM; PED; ACOM; interface velocity; absolute stability